


You're Not Alone

by knowmeknot



Category: Undertale (Video Game)
Genre: Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Vagina (Undertale), Fontcest, Gratuitous Soul Sex, Multi, Multiple Orgasms, Post-Undertale Neutral Route - King Mettaton Ending, Sensory Deprivation, Soul Sex, Spitroasting, Threesome
Language: English
Status: Completed
Published: 2017-02-04
Updated: 2017-02-04
Packaged: 2018-09-21 22:55:55
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,642
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9570497
Author URL: https://archiveofourown.org/users/knowmeknot/pseuds/knowmeknot
Summary: Mettaton and Papyrus are happily together. Papyrus notices that Sans has an interest in them but is unwillingly to admit it. Well they couldn't have that. After all,  the more monsters that loved Mettaton, the better. Gratuitous smut ahead.





	

**Author's Note:**

  * For [undertailsoulsex](https://archiveofourown.org/users/undertailsoulsex/gifts).



> Ecto-stuff have always been a bit hit or miss with me but combining it with soul sex? Hot damn! Why isn't there more of that in fanfiction?! Also, I can't believe I wrote this. But you write what you want and, uh, let's say this was a passing interest to me after all the JP fanart I've seen of similar concepts. This is also for Soul since she recognized the need for more of this threesome.
> 
> My tumblr is knowmeknot101.tumblr.com if you have a request or just want to chat. :]
> 
> Also, I dislike changing POV within the same one-shot but I did it here, sorry. ---- indication for change in POV.

Mettaton always considered himself an accommodating and open monster, so when Papyrus brought up the idea of including his brother in their relationship, he accepted the skeleton’s preposition. After all, the more monsters that loved him, the better it was for him as King of the Underground. And it wasn’t as if he disliked the short comedian. In fact, he found Sans to be quite charming, as long as he wasn’t pulling off his whoopee cushion pranks or slacking off at his job as his agent. Mettaton even had to admit that Sans’s comedy routines at his own resort were hilarious. And despite his laziness, Mettaton did appreciate when Sans meticulously took care of his mechanical issues and maintenance now that Alphys was gone.

The other reason he’d accepted was because he knew how much Papyrus loved his brother. He and Papyrus had been dating for several months now, shortly after the tall skeleton had become his personal agent, and although they are as happy as any loving couple, Papyrus oftentimes voiced his concerns about his brother. Mettaton always believed that Papyrus was much brighter than monsters gave him credit for, especially when it came to matters about Sans. 

“MY BROTHER IS NOT AS GREAT OF AN ACTOR AS HE BELIEVES HE IS,” Papyrus commented to the robot during their dinner date.

“Oh? What do you mean, darling,” Mettaton encouraged. He noticed how Papyrus was wringing his arms in distraught, and it saddened him to see it.

“YOU SEE, MY BROTHERLY INSTINCTS ARE TELLING ME THAT SANS IS LONELY, DESPITE HIS CONSTANT DENIALS. I’VE SEEN HOW HE LOOKS AT US! I THINK HE LIKES BOTH OF US BUT IS AFRAID TO VOICE HIS DESIRES, LIKE HE ALWAYS DOES.”

“So what do you propose we do?” the show robot asked, a pulse of excitement rushing through him.

“WE SHOULD INVITE HIM IN OUR NEXT LOVE MAKING SESSION!” the tall skeleton proclaimed. “AND MAKE SURE HE FEELS SO GOOD THAT HE’LL FINALLY ADMIT HIS FEELINGS!”

Papyrus gave him a determined look. Who was Mettaton to deny his boyfriend this opportunity? Besides, this sounded like it could be fun; he’d always wanted to try being in a polyamorous relationship.

“Of course, darling, that’s a wonderful idea!” Mettaton leaned over and gave his boyfriend a passionate kiss. “I’m always opened to try new things!”

A week after Papyrus’s proposal, he and Mettaton set their carefully planned date in motion. They would first go out to dinner at the restaurant in the MTT Resort (of course since he didn’t have to pay at his own establishment) and then include Sans in their passionate love-making session. Said skeleton declined their date offer initially but after much insistence from both Papyrus and him (he’d made it an order as King), Sans acceded. 

Mettaton found it extremely easy to get along with the small skeleton and immensely enjoyed his company, making him wonder why he’d never bothered to interact with Sans more often in a non-work setting, especially since the skeleton was, not only his boyfriend’s beloved family, but also technically one of his trusted agents. Well, he would have to definitely make it up to him since he always strove to treat his favorite employees well with the exception of Burgerpants (what was his name again?). Anyone who annoyed him, however, could simply disappear for all he cared.

When Mettaton and his two agents arrived at the palace he’d redecorated to match his exquisitive tastes, he noticed an abrupt change in Sans’s behavior. Instead of his quick humor and easygoing nature, he seemed tense and almost nervous.

“Do not worry, darling,” Mettaton placed a comforting hand on the short monster’s back. “We’ll make your time here absolutely fabulous!”

Sans simply nodded and gave a strained smile. Once they reached Mettaton’s ornate bedroom with the king sized bed and a lush, pink loveseat, the robot was quick to catch Papyrus into a deep kiss. Mettaton slid his tongue into the tall skeleton’s mouth, a remote part of his mind thanking Alphys for giving him this lovely appendage. Papyrus quickly responded by summoning his own orange one, and the two appendages danced between their opened mouths, wrestling for control. The two groaned into each other, and Mettaton smirked upon seeing the deep orange blush across Papyrus’s cheeks. He was sure his own were flushed pinked.

Mettaton heard a soft step in his plush pink carpet and, from the corner of his eyes, saw Sans turning away, as if to leave. Well he couldn’t let his subject leave without having done anything. It would defeat the whole purpose of their meeting. The robot king broke his kiss with Papyrus and both of them seized Sans before he could disappear. 

“Now where do you think you’re going? We haven’t even started yet,” Mettaton whispered sensually where Sans’s right ear would’ve been if he had them. 

“YES, COME BROTHER, WE ARE NOT LEAVING YOU OUT!”

Papyrus grasped his brother around the middle and brought the two of them over to the large bed. Papyrus sat up with his back pressed against the bed’s headboard and pulled Sans into his lap. He gave Mettaton a wink of his right socket, and the robot slowly stalked over towards them with a hungry glint in his eyes. He would make sure to give them both the best time they’ll ever have, as their king and employer.

\---

Sans gasped as Papyrus’s gloveless hands slipped under his sweater and trailed lightly over his ribs. Meanwhile, Mettaton’s own cold, hard, metal hands ghosted up his tibia and fibula. The smaller skeleton shuddered and fidgeted in an attempt to escape from their ministrations, his cheekbones burning furiously, but Papyrus only tightened his grasp. 

When his brother and Mettaton requested that he join them on their date, he’d assumed it would only entail dinner and hanging out to catch a movie or something. He did not expect this, never something like _this_. Because although he loved his brother dearly, perhaps more than any sibling should, and found himself becoming drawn to Mettaton more and more each day, he’d come to accept the fact that he would always be alone. His brother and Mettaton were basically made for each other. He never dared to ask, to even think, about joining them. Why would they want someone like him in their relationship anyway? He would only mess things up for them.

Sans was abruptly brought out of his distressing thoughts when he felt Papyrus’s phalanges rubbing against the underside of his ribs. Sans’s breathing hitched, and a soft moan soon escaped him. Before he’d even realized it, his brother had slipped the sweater off his head. Just as he had, Sans regained enough control to detangle himself from them, panting slightly. His soul throbbed violently inside his chest, as if it would burst from behind his ribs. He couldn’t recognize if it was from anxiety or need.

“you, you guys are makin’ a mistake.”

Mettaton quirked an elegant eyebrow and frowned slightly in confusion, “Oh? How so? Papy and I were under the impression that you wanted this.”

He did want this, wanted it so bad that he’d even dreamt about it. But these two were happy together, and he would never want to ruin that happiness.

“nope. ‘m fine with keepin’ myself company, heh,” Sans replied as casually as he could. 

The other two stopped what they were doing and gazed intently at him, making him sweat. He was about to move to grab his stuff and leave when Papyrus suddenly stopped him, “PLEASE STOP LYING, BROTHER.” 

Sans faltered. Papyrus took that opportunity to grasp his older sibling’s hands. 

Mettaton placed a hand on Sans’s right shoulder and added, “We just want to make you feel good, to show you our appreciation, darling. Won’t you give us a chance?”

With Papyrus giving Sans his infamous puppy-eyed expression, which he could never deny, and Mettaton’s sultry leer, the short skeleton relented. They resumed their previous positions and continued their soft ministrations, Papyrus at his bare ribs and Mettaton trailing up his legs. But try as he might, Sans couldn’t get himself to relax. Every time he saw his brother and Mettaton give each other knowing gestures, he tensed, feeling like an intrusion. He was about to call it quits, for real this time, when something soft and red flooded his vision. He scrambled to remove it when a bony hand seized his tightly to stop him.

“PLEASE DON’T,” Sans heard a soft clack, as he felt Papyrus’s teeth meet his left hand. “THIS MAY HELP SO PLEASE LET US DO THIS FOR YOU!”

Not understanding how losing one of his major senses could make him relax, he simply nodded. He did trust them, wholeheartedly; he just didn’t trust himself. 

“Safe word, darling?”

“uh, ketchup.” Beads of sweat lined Sans’s forehead.

The robot gave a soft tut, “Of course that would be your safe word.” The tone was light, teasing. 

“REMEMBER TO SQUEEZE MY HAND TWICE IF YOU CAN’T VERBALIZE!” Papyrus added.

Sans shivered as he felt bone meet his spine. With his sight gone, his other senses seemed to go into overdrive. The creaking of the bed every time someone moved, the shifting of the soft, silk sheets underneath his bones, Papyrus’s fingers dancing down his spine while Mettaton’s tongue licked up his legs, they all hit him simultaneously. It was all so overwhelming, leaving him gasping and moaning wantonly. Never once did Papyrus let go of his left hand, grasped tightly together. 

“You should look at yourself, Sans, so needy. You could say it… drives me wild,” the show robot growled lowly. “And it seems I’m not the only one, isn’t that right, Papy?”

Sans heard Papyrus groan with desire. He let out a surprised yelp as his shorts were ripped unceremoniously off of him. It was immediately silenced as cold, hard lips met his teeth and a surprisingly soft appendage (coming from a robot after all) entered his mouth. By this time, his brother’s long phalanges had trailed down to his pelvis. Sans jolted when the fingers reached his sacrum. The mound of magic in his lower pelvic region swirled into a dripping blue pussy. A bony finger pressed into the magic just below his pubis, and slipped in and out of the wet folds, sending sparks of arousal through him.

Mettaton broke the kiss and began dragging his tongue slowly down each of Sans’s cervical vertebrae, making him gasp and tilt his head to one side to allow the robot more access. There was a sudden dip in the bed, and although his brother kept a firm grip on Sans’s hand, he sensed Papyrus move in front of him between his legs and lift up his femurs. A surprised cry ripped out of him as, without warning, something wet and slick moved in between the folds of his ecto-vagina.

Pleasure shot through him like a current of electricity in copper wire. His brother’s tongue darted deep within him, occasionally peeking back out to flick at his clitoris, while Mettaton’s teasing of his neck continued. Trapped as he was between them, Sans could do nothing but accept everything he was being giving. All the touches were so much stronger, so much more pronounced, with his sight gone. Before long, his peak rapidly approached.

“hnngh, ah… hah… i’m gonna…” the small skeleton panted harshly. The assault continued with increased fervor, and with the way his brother’s tongue rubbed at his nub, he came with a cry, his back arching off the bed.

Both tongues left his body as he slowly came down from his high. The sound of deep and messy kissing reached his nonexistent ears, coming from above him. He reached a shaky right hand, his left still within Papyrus’s grasp, and felt Mettaton’s hard, metal body knelt behind him. They finally broke apart, gasping breathily. Sans turned his head back and forth, wondering what the two were up to next.

“Oooh Sans~,” the robot purred against the side of his head. “You taste simply… marvelous. Just as good as your brother.”

Sans felt heat rise to his face and, before he got the chance to reply, he heard whispers coming from above him followed by a shifting of clothes and a choked moan from Papyrus.

“AH! METTA...TON!” Desire and arousal dripped from his brother’s tone.

“pap, what’s goin’ on?” A spike of anxiety shot through him, and he spun his head around towards his brother’s voice. Did he do something wrong? 

His worries were immediately quenched when Mettaton placed his right hand onto something soft and wet. Sans moved his fingers around the surface, drawing out more desperate cries from Papyrus. Sans froze, realizing he was _touching his brother’s soul_. He was about to respond back when metal fingers suddenly brushed within his ribcage.

“Sans, can you summon your soul as well? I promise I’ll do it no harm,” Mettaton asked. 

The smallest monster hesitated, wondering if he was really willing to share something so personal with these two. It didn’t take long for him to realize that, yes, he was. He loved them both dearly, and despite his reservations about Mettaton’s intentions, Sans believed his employer’s words.

Sans gasped and groaned as his soul was caressed and moved with care. It must’ve been very close to his brother’s; he could feel Papyrus’s warm magic wash over his own cooler one. 

“Papyrus darling,” Sans could practically hear the smirk in Mettaton’s breathy tone. He shuddered violently and moaned softly as the robot’s metal hand press slightly against his soul. “How much do you trust me with what I’m about to do with both of your beautiful souls?”

Only noises of arousal and pleasure came from his younger brother, making Sans whimper out, “d-do whatever. i don’t care. just do something already!”

“Well aren’t you being rather demanding.” The bed mattress dipped behind him to his front between his legs, most likely Mettaton getting into position. “Well my desire and passion can’t wait any longer!” Mettaton swiftly brought his and his brother’s throbbing souls together and shoved them into his pussy.

Sans screamed and heard his brother do the same. His entire body convulsed violently as the walls of his cunt contracted, pressing against the two souls in ways he couldn’t even imagine. White hot pleasure flooded every inch of his mind and being, parts that he didn’t even know could feel good. He could sense Papyrus’s own pleasure, feeling more intimately connected with him than ever before; his brother’s love, adoration and devotion poured over him like rain in a thunderstorm. His peak approached within seconds for the second time that night. He wailed loudly, grinding his hips against the silk sheets, as he came. Soul fluid and cum flooded his pussy, some leaking out down his legs. Papyrus’s own blissful cry filled his ears. Both of them were left panting and shuddering from the afterglow.

“Did you think this was it, darling? The show still has its final act!”

Metal hands suddenly grabbed him and shifted him onto his hands and knees, jostling the two pulsing souls inside him. He couldn’t take it anymore; he wanted to see, no longer caring what the two monsters did in front of him, knowing already their feelings towards him. He just wanted to see them!

“ahh~, p-please, please let me see!” the small skeleton pleaded, still trembling from the aftershocks of his latest orgasm. “i-i want to see you two.”

With a dip in the mattress and metal fingers quickly brushing against the back of his head, light suddenly flooded his vision, temporarily blinding him. His brother’s red scarf fell away from his head. Sans hazily peered around until his eyes fell upon his brother, naked and leaning back against the headboard with his legs spread out and right hand pumping eagerly at his glowing long erection. Orange dusted his cheek as he gave Sans a lustful, hungry look, sockets lidded. 

Mettaton leaned over him and whispered, “Why don’t you pay your brother back for that wonderful job he did earlier.”

Sans groaned and slowly crawled over to his younger sibling, keening desperately with every movement that buffeted the souls and sent waves upon waves of arousal throughout his entire being. By the time he finally reached over to Papyrus, his quivering arms gave out. He fell, his brother’s long,orange cock in front of his face. He shakily licked up the length before commenting, “ah, pap… that’s quite a… ah… _boner_.”

“SAAANS!” the tall skeleton whined and canted his hips upwards so that his cock brushed against Sans’s cheekbone.

“Tsk, darling, killing the mood like that again will get you in trouble.” 

As if to prove it, Mettaton rutted his cock against Sans’s opening, pushing their souls deeper into his cunt. Both brothers gasped sharply. Sans felt his walls contract just enough to press the edges of the heart-shaped organs stuck within him but not enough to relieve him. He needed more stimulation, more movement, to come again!

“SANS PLEASE!”

His brother couldn’t wait any longer, and he couldn’t wait any longer either. Without a moment’s hesitation, Sans went down on his brother, taking in as much of Papyrus’ cock as he could. He conjured a throat to make the process less painful and more pleasant for both of them. He slowly worked his way down, licking the glowing shaft, until he was able to take his brother’s entire length. After taking a second to adjust for Papyrus’s size, he began bobbing his head rhythmically up and down. His brother mewled and jerked his hips upward, making Sans gag slightly. Papyrus suddenly froze in concern but Sans gave him a wink to continue.

The bed shifted, and Sans heard Mettaton move close behind him. A muffled cry escaped from him as the robot pushed his hard cock into Sans.

Oh stars. He had never felt this full and was stretched to his very limit. 

Mettaton, thankfully, gave him ample time to adjust. The robot hilted as much as he could into Sans’s pussy, pressing into both souls enough to send overwhelming pleasure within both skeletons. Mettaton and Papyrus moaned loudly, and the tall skeleton bucked his hips in response, forcing Sans back to take in more of Mettaton’s length. 

Mettaton set a steady pace thrusting into Sans, who tried to time Mettaton’s thrusts against Papyrus’s. He eventually found it to be too much effort and allowed the two of them to lead, letting himself get lost in the feeling of being taken by both ends. It didn’t take long for him to reach his peak, and another orgasm tore through him, filling his cunt with more cum and soul fluid. His clenching walls pressed their souls together, and Papyrus came inside his mouth. He swallowed as much of Papyrus’s cum as he could, though some of it dribbled out the corner of his mouth. Papyrus finally pulled out of him. With his mouth finally free, Sans uttered a groan, Mettaton still plowing into him with reckless abandon. His brother leaned back against the headboard and stroked his hand softly down Sans’s face.

The robot’s cries grew louder and more lewd, and a bright glow illuminated the room. A whimper escaped from Sans’s mouth as Mettaton suddenly pulled him upright, and pressed him flush against his metallic chest. Both skeletons groaned as Sans’s new position had Mettaton’s cock reaching deeper within him, hitting the center of their souls. Something wet dripped onto the top of his head, and when he looked up, Mettaton’s own soul hovered above his head.

“Hah... Papy darling,” the robot intoned breathlessly. “Come here… and help me… please.”

Sans watched as Papyrus shambled over, gingerly grasped Mettaton’s soul within his large hands and began massaging it with great care. He then gave it a few sensual licks before placing it into his mouth and kissing Mettaton with it still in there. Whatever was happening in their mouths must’ve been amazing, as Mettaton thrusted deeply within Sans, hitting that sensitive spot within his ectoplasmic vagina. Sans wailed as his walls tightened and was sent over the edge again for the fourth time that evening, Papyrus soon following after again as well. Mettaton suddenly stopped, and Sans felt his cock pulse.

“OH YEEEEESSSSS~!!!” Mettaton screamed in pure ecstasy as he came hard within Sans, who keened weakly at all the cum and soul fluid stuffed within him. He didn’t know how he’d done it but it left him almost uncomfortably full. 

After several seconds, the robot finally pulled out, eliciting a relieved gasp from Sans as everything seemed to gush out of him from his upright position. Mettaton’s arm was the only thing keeping him from collapsing into a boneless (heh) heap. His and Papyrus’s souls were last to come out.

With his soul back in its rightful place and the afterglow of his orgasms faded, exhaustion seeped into him. Both Papyrus and Mettaton eased him into a prone position and snuggled on either side of him. He was glad that soul magic and any residue left over would disappear on their own with time. No need for cleanup was always good news for a lazybones like him.

“Well, how was that, darling?” Mettaton’s hair was disheveled and his dark makeup smeared across his metal face.

“great, best time i’ve ever had. thanks guys,” Sans mumbled drowsily.

“I’M GLAD, BROTHER. I HOPE YOU NOW REALIZE THAT WE BOTH LOVE YOU VERY MUCH!” Papyrus beamed. 

“Yes, and we are always opened to have you in our relationship!”

Sans barely registered those words but nodded nevertheless. He’ll just ask them to repeat it in the morning. For now, he drifted off to sleep in the warm embrace of his two favorite monsters.


End file.
